John McDaniel, who conducts, composes and kibitzes for "The Rosie O'Donnell Show," was flying back from California recently when a stewardess came up to him and made his day. "I must tell you," she happily confessed, "I used to fly in and out of New York all the time and not go to Broadway shows. Since I've been watching 'Rosie,' I go all the time."

The subtext of this true story sets his heart to singing. "It just made me realize that that's what it's all about," he beams, "bringing Broadway into living rooms in Des Moines and Cincinnati and Flagstaff. It's thrilling to be able to spread that good stuff around."

If Rosie O'Donnell is the talk-show hostess with the mostes' on the ball -- Broadway's ambassador to the real world out there -- then McDaniel is the man in the pit, ruling the orchestrations. Their anthem is "We Go Together" (from Grease!, which marked both of their Broadway debuts), and indeed they've gone on to two Tony Awards shows (with McDaniel providing special material) -- and they continue to go on every weekday via her syndicated television series.

"I always imagined myself being a music director on Broadway -- and being happy at that," he admits. "Then, when the talk show came up, Rosie asked me if I'd like to be involved. I had never imagined myself being on TV or in a talk-show environment, but of course I said I'd love to -- and then I thought, 'What have I done? How am I am going to do that?'"

Very nicely and very naturally, it turns out -- and for this he credits Rosie herself. "It comes from the top. She's so relaxed, so comfortable, that it puts everyone at ease. Sometimes guests come out and think they're going to be nervous, and they wind up having a great time because she just puts you at ease. There's really no pretense with Rosie O'Donnell." Rosie O'Donnell Show" was a sixth-grade edition of, aptly, The Music Man -- but he was not, as you might have thought, the leader of a boys' band. He was Jacey Squires, the tenor in the barbershop quartet that ambled harmoniously through the show. "It was a small part, but it was so much fun," he recalls. "After that, I started checking out the records at the Kirkwood Library in St. Louis, where I'm from -- at least four a week -- and listening to them over and over. I'd listen to Kwamina and Kean and Plain and Fancy, and I'd learn all of the words."

Such show-tune intensity at an impressionable age has served him well later in life when he'll bring on Rosie's guests with a musical pun or some forgotten evergreen. "One of my favorites was when Dennis Miller was on the show, and I played 'The Miller's Son' from A Little Night Music. Nobody knew but a few people, but it's fun to do that."

As if five syndicated hours a week weren't enough to keep him busy, McDaniel miraculously found time last year to wave the baton over the Broadway company of Chicago, while its regular conductor, Rob Fisher, took a vacation. "It was an exhilarating time," as he remembers it. "I'd do 'Rosie' in the morning, take a nap and then do Chicago on Broadway."

Of course, the Kander-and-Ebb score was not the Chinese water-torture test, and he did have previous experience in the Chicago pit, having conducted a Long Beach Civic Light Opera production of it, which had a couple of key elements (Ann Reinking's choreography, Bebe Neuwirth's Velma) that five years later ignited its Encores! reprise and subsequent Tony-winning run. McDaniel also conducted another Long Beach lollapalooza that had an East Coast echo -- the original cast reunion of Company.

Barry and Fran Weissler, the producers whose Grease! brought McDaniel to Broadway, have first-call on his time and talent -- he's next scheduled to do their Bernadette Peters revival of Annie Get Your Gun -- but the other shows they've sent him out on haven't made it back to the Main Stem. The clapping for Applause stopped on the road, despite Stefanie Powers for a star, Gene Saks for a director and the original creators going into overtime trying to update the piece.

"It just wasn't meant to be revived," McDaniel reasons. "You never know when you start out on a project, but nevertheless it was a great experience working with them. Gosh! Comden and Green, what history they are -- living history, just walking around."

Then there was Busker Alley, which came to an abrupt dead end in Tampa when Tommy Tune broke his foot. "I was conducting the orchestra, and I saw it happen. It was right at the end of the show. He came down off a pole and landed wrong, and his face just went white. I'll never forget it. He just stood there, and the curtain came down. They had to carry him out for his bow; then he went to the hospital. Tommy was such a trouper, though, he continued to do the show with a cast on his ankle and foot. Our choreographer, Jeff Calhoun, came out in the same costume and did the dancing sections, while Tommy did all the acting and singing, hobbling around. It was remarkable."

McDaniel will also always have time for Patti LuPone. "We've worked together for a long time, and I especially loved doing her show, Patti LuPone Live, out in L.A. Like Rosie, she gives 180 percent all the time. She'll never walk through it. Patti is committed to a standard of excellence at every turn, and you have to rise to it just to keep up with her."

Although conducting occupies the prime part of his time, composing is quietly crawling ahead of it on his list of private priorities. Every note on "The Rosie O'Donnell Show" that's not from a Broadway score is his doing, including the opening theme. Right now, he is on the brink of breaking into his own Broadway score and, accordingly, has been interviewing potential lyricists. "I think I'm going to give it a go," he admits shyly.

For that teen-age show-tune fanatic a long time ago back in St. Louis, this would certainly complete the musical cycle. Move over, Kean and Kwamina -- herrrre's Johnny!

-- By Harry Haun